Tapeworm infection is the infestation of the digestive tract by a species of parasiticcestodalflatworm called tapeworms. Live tapeworm larvae (coenuri) are sometimes ingested by consuming undercooked meat. Once inside the digestive tract, a larva can grow into a very large adult tapeworm. Additionally, many tapeworm larvae cause symptoms in an intermediate host. For example, cysticercosis is a disease involving larval tapeworms in the human body.

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Although tapeworms in the intestine usually cause no symptoms, some people experience upper abdominal discomfort, diarrhea, and loss of appetite.[1]Anemia may develop in people with the fish tapeworm. Infection is generally recognized when the infected person passes segments of proglottids in the stool (looks like white worms), especially if a segment is moving.

Rarely, worms may cause obstruction of the intestine. And very rarely, T. solium larvae can migrate to the brain causing severe headaches, seizures and other neurological problems. Neurocysticercosis can progress for years before the patient displays symptoms.

Tapeworm eggs are generally ingested through food, water or soil contaminated with human or animal (host) faeces. For example, if a pig is infected with a tapeworm, it may pass eggs or segments (proglottids) of the adult tapeworm through its faeces into soil. Each segment contains thousands of microscopic tapeworm eggs. These eggs can be ingested via food contaminated with the faeces. Once the eggs have been ingested, they develop into larvae, which can migrate out of the intestines and form cysts in other tissues such as the lungs or liver. This type of infection is not common with beef or fish tapeworms, but can occur with the pork tapeworm — called cysticercosis — and can also occur with dog and sheep tapeworms — called echinococcosis.

Tapeworm infection can also be caused by eating raw or undercooked meat from an animal that has the larval form of the tapeworm cysts in its muscle tissue. Once ingested, the larvae then develop into adult tapeworms in the intestines. Adult tapeworms can measure up to 55 feet (17 m) long and can survive as long as 25 years. Some tapeworms attach themselves to the walls of the intestine, where they cause irritation or mild inflammation, while others may pass through to the stool and exit the body. Unlike other tapeworms, the dwarf tapeworm can complete its entire life cycle — egg to larva to adult tapeworm — in one host. This is the most common tapeworm infection in the world and can be transmitted between humans. Even while being treated for certain tapeworm infections, reinfection can result from ingesting tapeworm eggs shed by the adult worm into the stool, as a result of insufficient personal hygiene.

Among the most common tapeworms in humans are the pork tapeworm (T. solium), the beef tapeworm (T. saginata), the fish tapeworm (Diphyllobothrium spp.), and the dwarf tapeworm (Hymenolepis spp.). Infections involving the pork and beef tapeworms are also called taeniasis. Tapeworms of the genus Echinococcus infect and cause the most harm to intermediate hosts such as sheep and cattle. Infection with this type of tapeworm is referred to as Echinococcosis or hydatid disease. Symptoms vary widely, as do treatment options, and these issues are discussed in detail in the individual articles on each worm. With a few notable exceptions like the fish tapeworm, most cestodes that infect humans and livestock are cyclophyllids, and can be identified as such by the presence of four suckers on their scolex or head.